This tutorial review gives a synthetic chemistry perspective of magnetic relaxation phenomena through the lens of the reaction-coordinate diagram.

This report details how the design of specific nuclear-spin patterns on ligands modulates spin-relaxation times in a set of open-shell vanadium(iv) complexes.

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A detailed understanding of how counterion methyl groups affect electron spin relaxation is key to using these chemical species in the design of new molecular qubits. Here, we study the coherent spin dynamics of the V(IV) complex [V(C 6 H 4 O 2 ) 3 ] 2− with five different countercations: (Et 3 NH) + (1), (n-Bu 3 NH) + (2), (n-Bu 3 N− 2 H) + (2-d 2 ), (n-Hex 3 NH) + (3), and (n-Oct 3 NH) + (4). These counterions systematically increase the distance between the V(IV) spin and the methyl group of the alkyl chains. Pulsed electron paramagnetic resonance investigations in both glassy solutions and solid-state dilutions show that (1) the counterions are bound via hydrogen bonding to the [V(C 6 H 4 O 2 ) 3 ] 2− unit, even in frozen solutions, and that (2) the methyl group of the counterion has a dominant role in dictating the spin−spin (or phase memory) relaxation. We can reproduce the rate of the spin echo decay with a model that is based on the distance-dependent impact of the counterion methyl groups, and we note that in 1, the methyl groups generate a modulation of the echo decay. We also show that an important instrumental setting of the spin echo measurement, the shot repetition time, can have a dramatic impact on the shape of the echo decay curve and thus the measured relaxation times. Finally, the spin−lattice relaxation times are independent of cation and are the same, within experimental uncertainty, in glassy o-terphenyl and in the V(IV) complexes doped into the closed-shell Ti(IV) analogue, (n-Bu 3 NH) 2 [Ti-(C 6 H 4 O 2 ) 3 ] (2-Ti). Together, these data provide a mechanistic picture of how counterion CH 3 groups modulate phase memory spin relaxation in open-shell metal complexes.

Interstitial patterning of nuclear spins is a nascent design principle for controlling electron spin superposition lifetimes in open-shell complexes and solid-state defects. Herein we report the first test of the impact of the patterning principle on ligand-based nuclear spin dynamics. We test how substitutional patterning of 1H and 79/81Br nuclear spins on ligands modulates proton nuclear spin dynamics in the ligand shell of metal complexes. To do so, we studied the 1H nuclear magnetic resonance relaxation times (T 1 and T 2) of a series of eight polybrominated catechol ligands and six complexes formed by coordination of the ligands to a Ti­(IV) ion. These studies reveal that 1H T 1 values can be enhanced in the individual ligands by a factor of 4 (from 10.8(3) to 43(5) s) as a function of substitution pattern, reaching the maximum value for 3,4,6-tribromocatechol. The T 2 for 1H is also enhanced by a factor of 4, varying by ∼14 s across the series. When complexed, the impact of the patterning design strategy on nuclear spin dynamics is amplified and 1H T 1 and T 2 values vary by over an order of magnitude. Importantly, the general trends observed in the ligands also match those when complexed. Hence, these results demonstrate a new design principle to control 1H spin dynamics in metal complexes through pattern-based design strategies in the ligand shell.

Methods of controlling spin coherence by molecular design are essential to efforts to develop molecular qubits for quantum information and sensing applications. In this manuscript, we perform the first studies...